Genetically 'improved' oysters 'behind France's shellfish plague'

Genetically "improved" oysters could be behind the worst plague of the shellfish to hit France in 40 years, it has been reported.

By Henry Samuel in Paris

6:35PM BST 31 Aug 2008

Last month farmers around France announced that they had lost between 40 and 100 per cent of their oysters aged one to two years old.

According to oysters farmers cited by weekly magazine Marianne, the culprit is the triploid oyster, which is modified to give it three pairs of chromosomes instead of two, as is the case with common oysters.

"It's the triploid's fault", one was quoted as saying. "But one mustn't say that because the scientific and financial stakes are considerable".

According to Marianne, a disease linked to the triploid could have spread to non-modified oysters in offshore parks, although it gave no further details.

A growing number of oyster farmers favour the triploid, introduced into France in 1999, as it is grows much faster than other types and is sterile.

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This means the oyster never becomes milky and mushy, as is the case with normal oysters in their reproductive period.

This covers the summer months - hence the tradition of not eating oysters in months that do not contain the letter "r".

Many farmers have stopped growing normal oysters, which take up to four years to reach maturity.

Ifremer, which introduced the triploids, also known as "four season oysters", insists that they pose no danger to the environment. But its website warns that "broodstock should be maintained in a confined environment in order to hamper dissemination.

"This precautionary measure is essential since the potential environmental impact of the release of tetraploid in the natural environment is still unknown".

Triploids, commonplace among the Pacific oysters of North America, are not genetically modified in the strict sense of the term, as no genes from other species are transferred into their genetic material.

They are the produce of a process known as polyploidization, where the number of chromosome sets transmitted by the parents to their offspring is increased.

However, there was furious debate in France in 2000 when they were first introduced.

"Shellfish are among the last natural products that exist", Goulven Brest, head of France's shellfish committee told Libération newspaper at the time. "To lose that image would be extremely worrying. And what if they are nor (sterile). We consider this a risk".

The oyster crisis will have no impact on current oyster consumption, as the ready-to-eat, mature specimens have not been affected.

France is Europe's biggest oyster producer and the world's fourth behind China, Japan and South Korea.